/** * KeyedCoalescingWorker - A keyed worker that keeps only the latest value per key. * * Enqueues for an active or already-queued key are merged atomically instead of * creating duplicate queued items. `drainKey()` resolves only when that key has * no queued, pending, or active work left. * * @module KeyedCoalescingWorker */import type { Scope } from "effect";import { Effect, TxQueue, TxRef } from "effect"; export interface KeyedCoalescingWorker<K, V> {  readonly enqueue: (key: K, value: V) => Effect.Effect<void>;  readonly drainKey: (key: K) => Effect.Effect<void>;} interface KeyedCoalescingWorkerState<K, V> {  readonly latestByKey: Map<K, V>;  readonly queuedKeys: Set<K>;  readonly activeKeys: Set<K>;} export const makeKeyedCoalescingWorker = <K, V, E, R>(options: {  readonly merge: (current: V, next: V) => V;  readonly process: (key: K, value: V) => Effect.Effect<void, E, R>;}): Effect.Effect<KeyedCoalescingWorker<K, V>, never, Scope.Scope | R> =>  Effect.gen(function* () {    const queue = yield* Effect.acquireRelease(TxQueue.unbounded<K>(), TxQueue.shutdown);    const stateRef = yield* TxRef.make<KeyedCoalescingWorkerState<K, V>>({      latestByKey: new Map(),      queuedKeys: new Set(),      activeKeys: new Set(),    });     const processKey = (key: K, value: V): Effect.Effect<void, E, R> =>      options.process(key, value).pipe(        Effect.flatMap(() =>          TxRef.modify(stateRef, (state) => {            const nextValue = state.latestByKey.get(key);            if (nextValue === undefined) {              const activeKeys = new Set(state.activeKeys);              activeKeys.delete(key);              return [null, { ...state, activeKeys }] as const;            }             const latestByKey = new Map(state.latestByKey);            latestByKey.delete(key);            return [nextValue, { ...state, latestByKey }] as const;          }).pipe(Effect.tx),        ),        Effect.flatMap((nextValue) =>          nextValue === null ? Effect.void : processKey(key, nextValue),        ),      );     const cleanupFailedKey = (key: K): Effect.Effect<void> =>      TxRef.modify(stateRef, (state) => {        const activeKeys = new Set(state.activeKeys);        activeKeys.delete(key);         if (state.latestByKey.has(key) && !state.queuedKeys.has(key)) {          const queuedKeys = new Set(state.queuedKeys);          queuedKeys.add(key);          return [true, { ...state, activeKeys, queuedKeys }] as const;        }         return [false, { ...state, activeKeys }] as const;      }).pipe(        Effect.tx,        Effect.flatMap((shouldRequeue) =>          shouldRequeue ? TxQueue.offer(queue, key) : Effect.void,        ),      );     yield* TxQueue.take(queue).pipe(      Effect.flatMap((key) =>        TxRef.modify(stateRef, (state) => {          const queuedKeys = new Set(state.queuedKeys);          queuedKeys.delete(key);           const value = state.latestByKey.get(key);          if (value === undefined) {            return [null, { ...state, queuedKeys }] as const;          }           const latestByKey = new Map(state.latestByKey);          latestByKey.delete(key);          const activeKeys = new Set(state.activeKeys);          activeKeys.add(key);           return [            { key, value } as const,            { ...state, latestByKey, queuedKeys, activeKeys },          ] as const;        }).pipe(Effect.tx),      ),      Effect.flatMap((item) =>        item === null          ? Effect.void          : processKey(item.key, item.value).pipe(              Effect.catchCause(() => cleanupFailedKey(item.key)),            ),      ),      Effect.forever,      Effect.forkScoped,    );     const enqueue: KeyedCoalescingWorker<K, V>["enqueue"] = (key, value) =>      TxRef.modify(stateRef, (state) => {        const latestByKey = new Map(state.latestByKey);        const existing = latestByKey.get(key);        latestByKey.set(key, existing === undefined ? value : options.merge(existing, value));         if (state.queuedKeys.has(key) || state.activeKeys.has(key)) {          return [false, { ...state, latestByKey }] as const;        }         const queuedKeys = new Set(state.queuedKeys);        queuedKeys.add(key);        return [true, { ...state, latestByKey, queuedKeys }] as const;      }).pipe(        Effect.flatMap((shouldOffer) => (shouldOffer ? TxQueue.offer(queue, key) : Effect.void)),        Effect.tx,        Effect.asVoid,      );     const drainKey: KeyedCoalescingWorker<K, V>["drainKey"] = (key) =>      TxRef.get(stateRef).pipe(        Effect.tap((state) =>          state.latestByKey.has(key) || state.queuedKeys.has(key) || state.activeKeys.has(key)            ? Effect.txRetry            : Effect.void,        ),        Effect.asVoid,        Effect.tx,      );     return { enqueue, drainKey } satisfies KeyedCoalescingWorker<K, V>;  });